Not applicable
Not applicable
This invention relates generally to real-time computer systems and more specifically to the software structure for such systems.
The control and operation of real-time computer systems typically require a communications software package to control the communications with external data sources and sinks, a database software package for controlling the storage, retrieval, and updating of system data, a transaction software package for controlling the execution of one or more applications, and an operating system that exercises overall control of the the individual software packages.
In the past, one of the problems that has hampered missionization or customization of software is the competition for computer throughput. Generally, in the case of embedded real-time software in an inertial navigation system for example, one portion of the software is common (and usually essential) to all applications while additional portions are added or customized to satisfy specific applications. If the common and custom software execute in the same processor, there will be an inevitable competition for throughput resources.
The operating system together with a system of priorities provides a solution to this problem in many instances. Another approach replaces the operating system with a means for software partitioning. Software partitioning provides a means for avoiding interaction between different portions of the software. However, the partitioning methods to date rely on an accurate accounting for the amount of time required to execute different tasks. If execution times differ from the plan, one task might xe2x80x9cstepxe2x80x9d on another leading to potentially catastrophic consequences. This is particularly a concern if a user designs and programs customized software to coexist with the essential common software.
The invention is a method and apparatus for repetitively executing a plurality of software packages at a plurality of rates utilizing a common set of computational resources. The method consists of counting contiguous time increments and executing a plurality of software packages. Each software package is executed during each time increment in one or more sequences of time increments. The time increments in each sequence recur at a predetermined rate, and the time increments assigned to one software package do not overlap the time increments assigned to any other of the plurality of software packages.
The method includes the case where a time increment is a sub-slot of a time slot, a time slot containing a plurality of sub-slots. In this case, one and only one software package is assigned to a sub-slot for execution. A software package can be programmed to execute during any number of sub-slots in a time slot. A software package can also be programmed to execute at two or more rates.